A germline transgenic silkworm that secretes recombinant proteins in the sericin layer of cocoon

Broad Complex-Z2 directly activates BmMBF2 to inhibit the silk protein synthesis in the silkworm, Bombyx mori

Silk proteins, as natural macromolecules, have extensive applications in biomaterials and biomedicine. In the silkworm, the expression of silk protein genes is negatively associated with ecdysone during the molt stage, while it is positively correlated with juvenile hormone during the intermolt stage. In our previous study, overexpression of an isoform Z2 of Broad Complex (BmBrC-Z2), an ecdysone early response factor, significantly reduced the expression of silk protein genes. However, the underlying regulatory mechanism remains unclear. In this study, we conducted transcriptomic analysis and found that overexpressing BmBrC-Z2 significantly upregulated the expression level of multiprotein bridging factor 2 (BmMBF2), an inhibitor of fibroin heavy chain (FibH). Further investigations revealed that BmBrC-Z2 directly regulated BmMBF2 by binding to cis-regulatory elements, as demonstrated using Dual-Luciferase Reporter Gene Assay, EMSA, and ChIP-PCR assay. Additionally, when using the CRISPR/Cas9 system to knock out BmMBF2, silk protein genes were significantly upregulated during the molt stage of mutant larvae. These findings uncover the negative regulation of silk protein synthesis by the ecdysone signaling cascade, specifically through the manipulation of BmMBF2 expression during the molt stage. This study enhances to our understanding of the temporal regulatory mechanism governing silk protein synthesis and offers a potential strategy for improving silk yield.

Highly efficient expression of human extracellular superoxide dismutase (rhEcSOD) with ultraviolet-B-induced damage-resistance activity in transgenic silkworm cocoons

Extracellular superoxide dismutase (EcSOD) protects tissues from oxidative stress, and thus is considered as a therapeutic agent for many diseases such as atherosclerosis, hypertension, and cancer. However, cost-effective production of bioactive recombinant human EcSOD (rhEcSOD) remains a challenge. Herein, we developed an efficient strategy for producing active rhEcSOD by transgenic silkworms. rhEcSOD was successfully synthesized as homodimers and homotetramers in the middle silk gland and spun into the cocoons with a concentration of 9.48 ± 0.21 mg/g. Purification of rhEcSOD from the cocoons could be conveniently achieved with a purity of 99.50% and a yield of 3.5 ± 0.5 mg/g. Additionally, N-glycosylation at the only site of N89 in rhEcSOD with 10 types were identified. The purified rhEcSOD gained the potent enzymatic activity of 4 162 ± 293 U/mg after Cu/Zn ions incorporation. More importantly, rhEcSOD was capable of penetrating and accumulating in the nuclei of cells to maintain cell morphology and attenuate ultraviolet B-induced cell apoptosis by eliminating reactive oxygen species and inhibiting the C-Jun N-terminal kinase signaling pathway. These results demonstrated that the transgenic silkworm could successfully produce rhEcSOD with enzymatic and biological activities for biomedical applications.

TALEN-mediated homologous-recombination-based fibroin light chain in-fusion expression system in Bombyx mori

Silkworm was the first domesticated insect and has important economic value. It has also become an ideal model organism with applications in genetic and expression studies. In recent years, the use of transgenic strategies has made the silkworm silk gland an attractive bioreactor for the production of recombinant proteins, in particular, piggyBac-mediated transgenes. However, owing to differences in regulatory elements such as promoters, the expression levels of exogenous proteins have not reached expectations. Here, we used targeted gene editing to achieve site-specific integration of exogenous genes on genomic DNA and established the fibroin light chain (FibL) in-fusion expression system by TALEN-mediated homology-directed recombination. First, the histidine-rich cuticular protein (CP) was successfully site-directed inserted into the native FibL, and the FibL-CP fusion gene was correctly transcribed and expressed in the posterior silk gland under the control of the endogenous FibL promoter, with a protein expression level comparable with that of the native FibL protein. Moreover, we showed based on molecular docking that the fusion of FibL with cuticular protein may have a negative effect on disulfide bond formation between the C-terminal domain of fibroin heavy chain (FibH) and FibL-CP, resulting in abnormal spinning and cocoon in homozygotes, indicating a significant role of FibL in silk protein formation and secretion. Our results demonstrate the feasibility of using the FibL fusion system to express exogenous proteins in silkworm. We expect that this bioreactor system will be used to produce more proteins of interest, expanding the application value of the silk gland bioreactor.

Large-scale and cost-effective production of recombinant human serum albumin (rHSA) in transgenic Bombyx mori cocoons

HSA is considered a versatile natural cargo carrier with multiple bio-functions and applications. However, insufficient supply of HSA has limited widespread use. Although various recombinant expression systems had been applied to produce the rHSA to overcome the limited resource, cost-effective and large scale production of rHSA remains a challenge. Herein, we provide a strategy for the large-scale and cost-effective production of rHSA in cocoons of transgenic silkworms, achieving a final 13.54 ± 1.34 g/kg of rHSA yield in cocoons. rHSA was efficiently synthesized and stable over the long-term in the cocoons at room temperature. Artificial control of silk crystal structure during silk spinning significantly facilitated rHSA extraction and purification, with 99.69 ± 0.33 % purity and a productivity of 8.06 ± 0.17 g rHSA from 1 kg cocoons. The rHSA had the same secondary structure to natural HSA, along with effective drug binding capacity, biocompatibility, and bio-safe. The rHSA was successfully evaluated as a potential substitute in serum-free cell culture. These findings suggest the silkworm bioreactor is promising for large-scale and cost-effective production of high quality rHSA to meet the increased worldwide demand.

Sex separation by body color via a W-chromosome-linked transgene

Sex separation processes are important for commercial insect production and sterile insect techniques. Here, we describe the transgenic insertion of a DsRed expression cassette driven by the enhancer HR3 and strong promoter IE1 into the silkworm W chromosome as a dominant visible marker of sex separation. The obtained transgenic lines showed female-specific body color visible to the naked eye at the second- to fifth-instar larval, pupal and adult stages, and their performance traits were comparable to those of a nontransgenic practical silkworm variety. This strategy can greatly facilitate the sex separation of silkworms for male-only rearing and to obtain hybrids while avoiding sibling mating, and it can also be applied to the sex separation of other light-colored insects.

Dimmed gene knockout shortens larval growth and reduces silk yield in the silkworm, Bombyx mori

The bHLH domain transcription factor, Bombyx mori-derived dimmed (Bmdimm), is directly regulated by the JH-BmMet/BmSRC-BmKr-h1 pathway and plays a key role in regulating the expression of FibH, which codes the main component of silk protein. However, the other roles of Bmdimm in silk protein synthesis remain unclear. Here, we established a Bmdimm knockout (KO) line containing a 7-bp deletion via CRISPR/Cas9 system, which led to the absence of the bHLH domain. The expression level of silk protein genes and silk yield decreased significantly in the Bmdimm KO line. Moreover, knocking out Bmdimm led to shortened larval stages and significant weight loss in larvae and adults. Bmdimm was found to be highly expressed in the silk gland, but it was also expressed in the fat body. The expression level of Bmkr-h1 in the fat body was significantly downregulated in the Bmdimm KO line. Exogenous JHA treatment upregulated Bmkr-h1 and rescued the phenotype of larval growth in the Bmdimm KO line. In conclusion, knocking out Bmdimm led to a shortened larval stage via the inhibition of Bmkr-h1 expression, then reduced silk yield. These findings help to elucidate the regulatory mechanism of fibroin synthesis and larval development in silkworms.

Bioengineered silkworm model for expressing human neurotrophin-4 with potential biomedical application

Neurotrophin-4 (NT-4) is a neurotrophic factor that plays important roles in maintaining nerve cell survival, regulating neuronal differentiation and apoptosis, and promoting nerve injury repair. However, the source of sufficient NT-4 protein and efficient delivery of NT-4 remain a challenge. This study aims to express an activated human NT-4 protein in a large scale by genetically engineering silk gland bioreactor of silkworm as a host. We showed that the expression of human NT-4-functionalized silk material could promote proliferation of mouse HT22 cells when compared to the natural silk protein, and no obvious cytotoxicity was observed under the conditions of different silk materials. Importantly, this functional silk material was able to induce the potential differentiation of HT22 cells, promote peripheral neural cell migration and neurite outgrowth of chicken embryo dorsal root ganglion (DRG). All these results demonstrated a high bioactivity of human NT-4 protein produced in silk gland. Therefore, based on the silkworm model, the further fabrication of different silk materials-carrying active NT-4 protein with good mechanical properties and great biocompatibility will give promising applications in tissue engineering and neurons regeneration.

A Targeted In-Fusion Expression System for Recombinant Protein Production in Bombyx mori

The domesticated silkworm, Bombyx mori, is an economically important insect that synthesizes large amounts of silk proteins in its silk gland to make cocoons. In recent years, germline transformation strategies advanced the bioengineering of the silk gland as an ideal bioreactor for mass production of recombinant proteins. However, the yield of exogenous proteins varied largely due to the random insertion and gene drift caused by canonical transposon-based transformation, calling for site-specific and stable expression systems. In the current study, we established a targeted in-fusion expression system by using the transcription activator-like effector nuclease (TALEN)-mediated targeted insertion to target genomic locus of sericin, one of the major silk proteins. We successfully generated chimeric Sericin1-EGFP (Ser-2A-EGFP) transformant, producing up to 3.1% (w/w) of EGFP protein in the cocoon shell. With this strategy, we further expressed the medically important human epidermal growth factor (hEGF) and the protein yield in both middle silk glands, and cocoon shells reached to more than 15-fold higher than the canonical piggyBac-based transgenesis. This natural Sericin1 expression system provides a new strategy for producing recombinant proteins by using the silkworm silk gland as the bioreactor.

Effects of transgenic silk materials that incorporate FGF-7 protein microcrystals on the proliferation and differentiation of human keratinocytes

The silk glands of silkworms produce large quantities of fibroin, which is a protein that can be physically processed and used as a biodegradable carrier for cell growth factors in tissue engineering applications. Meanwhile, protein microcrystals known as polyhedra, which are derived from cypovirus 1, have been used as a vehicle to protect and release encapsulated cell growth factors. We report the generation of transgenic silkworms that express recombinant fibroblast growth factor-7 (FGF-7) fused with the polyhedron-encapsulating signal in polyhedra produced in the middle (MSG) and posterior (PSG) silk glands. Immunofluorescence showed that polyhedra from silk glands are associated with FGF-7. The MSG and PSG from transgenic silkworms were processed into fine powdery materials, from which FGF-7 activity was released to stimulate the proliferation of human keratinocyte epidermal cells. Powders from PSGs exhibited higher FGF-7 activity than those from MSGs. Moreover, PSG powder showed a gradual release of FGF-7 activity over a long period and induced keratinocyte proliferation and differentiation in 3D culture to promote the formation of stratified epidermis expressing positive differentiation marker proteins. Our results indicate that powdery materials incorporating the FGF-7-polyhedra microcrystals from silk glands are valuable for developing cell/tissue engineering applications in vivo and in vitro.

Transgenic Ectopic Overexpression of Broad Complex (BrC-Z2) in the Silk Gland Inhibits the Expression of Silk Fibroin Genes of Bombyx mori

Bombyx mori silk protein genes are strictly turned on and off in different developmental stages under the hormone periodically change. The broad complex (BrC) is a transcription factor mediating 20-hydroxyecdysone action, which plays important roles during metamorphosis. Here, we observed that two isoforms of BmBrC (BmBrC-Z2 and BmBrC-Z4) exhibited contrasting expression patterns with fibroin genes (FibH, FibL and P25) in the posterior silk gland (PSG), suggesting that BmBrC may negatively regulate fibroin genes. Transgenic lines were constructed to ectopically overexpress BmBrC-Z2 in the PSG. The silk protein genes in the transgenic line were decreased to almost half of that in the wild type. The silk yield was decreased significantly. In addition, the expression levels of regulatory factors (BmKr-h1 and BmDimm) response to juvenile hormone (JH) signal were inhibited significantly. Then exogenous JH in the BmBrC-Z2 overexpressed lines can inhibit the expression of BmBrC-Z2 and activate the expression of silk protein genes and restore the silk yield to the level of the wild type. These results indicated that BmBrC may inhibit fibroin genes by repressing the JH signal pathway, which would assist in deciphering the comprehensive regulation mechanism of silk protein genes.

Production of a correctly assembled fibrinogen using transgenic silkworms

Fibrinogen from human blood is used as a main component of coagulants, including surgical tissue sealants. The development of a recombinant human fibrinogen (rFib) is anticipated to eliminate the risks of blood-borne infections. Here, we report the efficient production of rFib in a transgenic silkworm system. A silkworm line carrying cDNAs of the fibrinogen Aα and γ chains (Aα/γ-silkworm) produced Aα and γ chains in its cocoons, however, the Bβ chains were not detected from cocoons of another silkworm line carrying the cDNA of fibrinogen Bβ chains (Bβ-silkworm). A silkworm line for all three fibrinogen chains was generated by crossing Aα/γ-silkworms with Bβ-silkworms, which secreted Aα₂Bβ₂γ₂ fibrinogen (rFib) into cocoons at high contents. The N-terminal amino acid sequences of the three rFib chains were identical to those of the corresponding chains of native fibrinogen (nFib). The N-glycan profile of the rFib comprised oligomannose-type (53%), complex-type (34%), and paucimannose-type (13%); neither high-mannose-type (six or more mannose residues) nor core-fucosylated glycans were observed. The coagulation activity of the rFib was evaluated for the amount of thrombin-released fibrinopeptide A (FpA) and the kinetics for turbidity increase (non-covalent network formation) in the solution. FpA release rates were equivalent between rFib and nFib; by contrast, the kinetics of the turbidity increase for rFib were accelerated nearly two-fold, for both the rate and maximum value, compared to those of nFib. These results demonstrate that the rFib produced in the transgenic silkworm system is comparable to nFib in both physical and coagulative properties. This rFib is a promising candidate component for safe hemostatic pharmaceuticals.

Functional characterization of the cis-regulatory region for the vitellogenin gene in Plutella xylostella

The vitellogenin gene promoter (VgP) is an essential cis-regulatory element that plays a significant role in transcription of the vitellogenin (Vg) gene, leading to the production of yolk protein in insects, including lepidopterans. However, the function of VgP is still not clear in Plutella xylostella. Here, we cloned a 5.1 kb DNA fragment of the cis-regulatory region adjacent to the 5' end of the Vg gene of P. xylostella (PxVg). We identified two promoter sites in that 5' upstream sequence of PxVg and performed in vitro analysis of two promoter sequences (PxVgP1, 4.9 kb, and PxVgP2, 2.9 kb) in the embryonic cell line of P. xylostella. PxVgP2 exhibited higher enhanced green fluorescent protein (EGFP) expression, so PxVgP2 was used for in vivo analysis. Strong EGFP fluorescence was observed in adult females and the fat body of females, with low expression in embryos. Our results suggest that PxVgP is an important stage-, tissue- and sex-specific endogenous cis-regulatory element in P. xylostella.

Effects of Osiris9a on Silk Properties in Bombyx mori Determined by Transgenic Overexpression

Osiris is an insect-specific gene family with multiple biological roles in development, phenotypic polymorphism, and protection. In the silkworm, we have previously identified twenty-five Osiris genes with high evolutionary conservation and remarkable synteny among several insects. Bombxy moriOsiris9a (BmOsi9a) is expressed only in the silk gland, particularly in the middle silk gland (MSG). However, the biological function of BmOsi9a is still unknown. In this study, we overexpressed BmOsi9a in the silk gland by germline transgene expression. BmOsi9a was overexpressed not only in the MSG but also in the posterior silk gland (PSG). Interestingly, BmOsi9a could be secreted into the lumen in the MSG but not in the PSG. In the silk fiber, overexpressed BmOsi9a interacted with Sericin1 in the MSG, as confirmed by a co-immunoprecipitation assay. The overexpression of BmOsi9a altered the secondary structure and crystallinity of the silk fiber, thereby changing the mechanical properties. These results provide insight into the mechanisms underlying silk proteins secretion and silk fiber formation.

Identification of a germline-expression promoter for genome editing in Bombyx mori

Identification of stage- and tissue-specific cis-regulatory elements will enable more precise genomic editing. In previous studies of the silkworm Bombyx mori, we identified and characterized several tissue- and sex-specific cis-regulatory elements using transgenic technology, including a female- and fat body-specific promoter, vitellogenin, testis-specific promoters, Radial spoke head 1 (BmR1) and beta-tubulin 4 (Bmβ4). Here we report a cis-regulatory element specific for a somatic and germ cell-expressed promoter, nanos (Bmnos). We investigated activities of three truncated promoter sequences upstream of the transcriptional initiation site sequences of Bmnos in vitro (nos-0.6kb, nos-1kb and nos-2kb) and in vivo (nos-2kb). In BmN cultured cells, all three lengths drove expression of the gene encoding enhanced green fluorescence protein (EGFP), although nos-2kb had the highest fluorescence activity. In transgenic silkworms, nos-2kb drove EGFP expression at the early embryonic stage, and fluorescence was concentrated in the gonads at later embryonic stages. In addition, this cis-regulatory element was not sex differentiated. The fluorescence intensity gradually weakened following the larval developmental stage in the gonads and were broadly expressed in the whole body. The nos-2kb promoter drove the Cas9 system with efficiency comparable to that of the broad-spectrum strong IE1 promoter. These results indicate that Bmnos is an effective endogenous cis-regulatory element in the early embryo and in the gonad that can be used in applications involving the clustered, regularly interspaced, short palindromic repeats (CRISPR)/Cas9 system.

A silkworm based silk gland bioreactor for high-efficiency production of recombinant human lactoferrin with antibacterial and anti-inflammatory activities

Background

Silk glands are used by silkworms to spin silk fibers for making their cocoons. These have recently been regarded as bioreactor hosts for the cost-effective production of other valuable exogenous proteins and have drawn wide attention.

Results

In this study, we established a transgenic silkworm strain which synthesizes the recombinant human lactoferrin (rhLF) in the silk gland and spins them into the cocoon by our previously constructed silk gland based bioreactor system. The yield of the rhLF with the highest expression level was estimated to be 12.07 mg/g cocoon shell weight produced by the transgenic silkworm strain 34. Utilizing a simple purification protocol, 9.24 mg of the rhLF with recovery of 76.55% and purity of 95.45% on average could be purified from 1 g of the cocoons. The purified rhLF was detected with a secondary structure similar with the commercially purchased human lactoferrin. Eight types of N-glycans which dominated by the GlcNAc (4) Man (3) (61.15%) and the GlcNAc (3) Man (3) (17.98%) were identified at the three typical N-glycosylation sites of the rhLF. Biological activities assays showed the significant evidence that the purified rhLF could relief the lipopolysaccharide (LPS)-induced cell inflammation in RAW264.7 cells and exhibit potent antibacterial bioactivities against the Escherichia coli (E. coli) and Bacillus subtilis.

Conclusions

These results show that the middle silk gland of silkworm can be an efficient bioreactor for the mass production of rhLF and the potential application in anti-inflammation and antibacterial.

Electronic supplementary material

The online version of this article (10.1186/s13036-019-0186-z) contains supplementary material, which is available to authorized users.

Genetically engineered bi-functional silk material with improved cell proliferation and anti-inflammatory activity for medical application

Functional silk is a promising material for future medical applications. These include fabrication of diverse silk fiber and silk protein-regenerated biomaterials such as silk sutures, hydrogel, films, and 3D scaffolds for wound healing and tissue regeneration and reconstruction. Here, a novel bi-functional silk with improved cell proliferation and anti-inflammatory activities was created by co-expressing the human basic fibroblast growth factor (FGF2) and transforming growth factor-β1 (TGF_β1) genes in silkworm. First, both FGF2 and TGF_β1 genes were confirmed to be successfully expressed in silk thread. The characterization of silk properties by SEM, FTIR, and mechanical tests showed that this new silk (FT silk) had a similar diameter, inner molecular composition, and mechanical properties as those of normal silk. Additionally, expressed FGF2 and TGF_β1 proteins were continuously and slowly released from FT silk for one week. Most importantly, the FGF2 and TGF_β1 contained in FT silk not only promoted cell proliferation by activating the ERK pathway but also significantly reduced LPS-induced inflammation responses in macrophages by mediating the Smad pathway. Moreover, this FT silk had no apparent toxicity for cell growth and caused no cell inflammation. These properties suggest that it has a potential for medical applications. STATEMENT OF SIGNIFICANCE: Silk spun by domestic silkworm is a promising material for fabricating various silk protein regenerated biomaterials in medical area, since it owes good biocompatibility, biodegradability and low immunogenicity. Recently, fabricating various functional silk fibers and regenerated silk protein biomaterials which has ability of releasing functional protein factor is the hot point field. This study is a first time to create a novel bi-functional silk material with the improved cell proliferation and anti-inflammatory activity by genetic engineered technology. This novel silk has a great application potential as new and novel medical material, and this study also provides a new strategy to create various functional or multifunctional silk fiber materials in future.

Insights into the repression of fibroin modulator binding protein-1 on the transcription of fibroin H-chain during molting in Bombyx mori

Fibroin modulator binding protein-1 (FMBP-1) is a novel DNA-binding protein containing a conserved score and three amino acid peptide repeat (STPR) domain. The roles of factors containing STPR domain are less known. Although multiple transcription factors are involved in the transcriptional regulation of silk protein genes during the development of silkworm, the mechanism of transcriptional repression of silk protein genes during molting remains unclear. Here, we found that FMBP-1 expression was contrary to that of fibroin heavy chain (fib-H) during the fourth molting period of Bombyx mori. FMBP-1 repressed fib-H promoter activity by directly binding to the -130 element in the fib-H promoter region. We also identified two proteins, Bmsage and Bmdimm, that interacted with FMBP-1 in the posterior silk gland of silkworm larvae, and further verified these interactions by far western blotting and microscale thermophoresis in vitro, as well as co-immunoprecipitation and bimolecular fluorescence complementation at the cellular level. The luciferase reporter assay showed that the interaction between FMBP-1 and Bmdimm antagonized the activation of Bmdimm on fib-H transcription, but did not affect FMBP-1-mediated transcriptional repression on fib-H gene. Therefore, we proposed the following mechanism of fib-H transcriptional repression by FMBP-1 during the molting of silkworm larvae: 1) FMBP-1 directly binds to the -130 element in the fib-H promoter to repress fib-H transcription; 2) FMBP-1 interacts with Bmdimm to antagonize the activation of Bmdimm on fib-H transcription. Our findings promote a better understanding of fib-H transcriptional regulation and provide novel insights into the transcriptional repression of fib-H by FMBP-1 and basic helix-loop-helix factors Bmdimm during the molting of silkworm larvae. Our study also provides valuable information regarding the biological function of factors containing STPR domain.

Novel recombinant feline interferon carrying N-glycans with reduced allergy risk produced by a transgenic silkworm system

Background

The generation of recombinant proteins for commercialisation must be cost-effective. Despite the cost-effective production of recombinant feline interferon (rFeIFN) by a baculovirus expression system, this rFeIFN carries insect-type N-glycans, with core α 1,3 fucosyl residues that act as potential allergens. An alternative method of production may yield recombinant glycoproteins with reduced antigenicity.

Results

A cDNA clone encoding the fifteenth subtype of FeIFN-α (FeIFN-α15) was isolated from a Japanese domestic cat. This clone encoded a protein of 189 amino acids with a molecular mass of 21.1 kDa. The rFeIFN-α15 was expressed using a transgenic silkworm system, which was expected to yield an N-glycan structure with reduced antigenicity compared with the protein produced by the baculovirus system. The resulting rFeIFN-α15 accumulated in the sericin layer of silk fibres and was easily extracted and purified by column chromatography. The N-terminal amino acid sequence of purified rFeIFN-α15 was identical to the mature form of natural sequence. Moreover, its N-glycans did not include detectable core α 1,3 fucosyl residues. Its anti-vesicular stomatitis virus activity (2.6 × 10⁸ units/mg protein) was comparable to that of the baculovirus-expressed rFeIFN.

Conclusions

The lower allergy risk of rFeIFN produced by the transgenic silkworm system than by the baculovirus expression system is due to the former lacking core α 1,3 fucosyl residues in its N-glycans. The rFeIFN-α15 produced by the transgenic silkworm system may be a prospective candidate for the next generation of rFeIFN in veterinary medicine.

Transgenic Silkworm-Based Silk Gland Bioreactor for Large Scale Production of Bioactive Human Platelet-Derived Growth Factor (PDGF-BB) in Silk Cocoons

Human platelet derived growth factor (PDGF) is a major therapeutic protein with great demand in the clinical setting; however, its rate of supply is far from meeting needs. Here, we provide an effective strategy to produce PDGF-BB in large quantities using a transgenic silkworm. The codon-optimized PDGF-B gene regulated by the highly efficient sericin-1 expression system was integrated into the genome of a silkworm. The high transcriptional expression of the PDGF-BB gene in the transgenic silkworm competitively inhibited the transcription expression of the endogenous sericin-1 gene which caused a significant 37.5% decline. The PDGF-BB synthesized in the middle silk gland (MSG) of transgenic silkworms could form a homodimer through intermolecular disulfide bonds, which is then secreted into sericin lumen and finally, distributed in the sericin layer of the cocoon. In this study, a protein quantity of approximately 0.33 mg/g was found in the cocoon. Following a purification process, approximately 150.7 μg of recombinant PDGF-BB with a purity of 82% was purified from 1 g of cocoons. Furthermore, the bioactivity assays showed that the purified recombinant PDGF-BB was able to promote the growth, proliferation and migration of NIH/3T3 cells significantly. These results suggest that the silk gland bioreactor can produce active recombinant PDGF-BB as an efficient mitogen and wound healing agent.

Transgenic silkworms secrete the recombinant glycosylated MRJP1 protein of Chinese honeybee, Apis cerana cerana

Major royal jelly protein-1 (MRJP1) is the most abundant glycoprotein of royal jelly (RJ) and is considered a potential component of functional foods. In this study, we used silkworm transgenic technology to obtain five transgenic silkworm lineages expressing the exogenous recombinant Chinese honeybee, Apis cerana cerana, protein-1 (rAccMRJP1) under the control of a fibroin light chain (Fib-L) promoter in the posterior silk glands. The protein was successfully secreted into cocoons; specifically, the highest rAccMRJP1 protein content was 0.78% of the dried cocoons. Our results confirmed that the protein band of the exogenous rAccMRJP1 protein expressed in the transgenic silkworm lineages was a glycosylated protein. Therefore, this rAccMRJP1 protein could be used as an alternative standard protein sample to measure the freshness of RJ. Moreover, we also found that the overall trend between the expression of the endogenous and exogenous genes was that the expression level of the endogenous Fib-L gene declined as the expression of the exogenous rAccMRJP1 gene increased in the transgenic silkworm lineages. Thus, by employing genome editing technology to reduce silk protein expression levels, a silkworm bioreactor expression system could be developed as a highly successful system for producing various valuable heterologous proteins, potentially broadening the applications of the silkworm.

Increasing the yield of middle silk gland expression system through transgenic knock-down of endogenous sericin-1

Various genetically modified bioreactor systems have been developed to meet the increasing demands of recombinant proteins. Silk gland of Bombyx mori holds great potential to be a cost-effective bioreactor for commercial-scale production of recombinant proteins. However, the actual yields of proteins obtained from the current silk gland expression systems are too low for the proteins to be dissolved and purified in a large scale. Here, we proposed a strategy that reducing endogenous sericin proteins would increase the expression yield of foreign proteins. Using transgenic RNA interference, we successfully reduced the expression of BmSer1 to 50%. A total 26 transgenic lines expressing Discosoma sp. red fluorescent protein (DsRed) in the middle silk gland (MSG) under the control of BmSer1 promoter were established to analyze the expression of recombinant. qRT-PCR and western blotting showed that in BmSer1 knock-down lines, the expression of DsRed had significantly increased both at mRNA and protein levels. We did an additional analysis of DsRed/BmSer1 distribution in cocoon and effect of DsRed protein accumulation on the silk fiber formation process. This study describes not only a novel method to enhance recombinant protein expression in MSG bioreactor, but also a strategy to optimize other bioreactor systems.

YorkieCA overexpression in the posterior silk gland improves silk yield in Bombyx mori

The traditional hybrid breeding techniques can no longer meet the increasing demands for silk production by the silkworm, Bombyx mori, and further improvement of the silk yield will depend on modern molecular breeding techniques. Here, we report improved silk yield in transgenic silkworms overexpressing the oncogene Yorkie^CA specifically in the posterior silk gland (PSG). The Yorkie^CA cDNA was ligated downstream of the hr3 enhancer and the fibroin L-chain (Fil) promoter, then inserted into a piggyBac vector for transgene. Overexpression of Yorkie^CA in the PSG significantly increased the weight of the PSG, and also increased the weight of the cocoon, larval body, and pupal body to decreasing degrees. Overexpression of Yorkie^CA up-regulated the Yorkie target genes resulting in increased cell size, endomitosis, the number of protein synthesis organelles, the expression of fibroin genes in the PSG, and eventually silk yield. Additionally, as we reported previously using the binary GAL4/UAS system, transgenic silkworms overexpressing Ras1^CA with the hr3 enhancer and the Fil promoter also showed improved silk yield. Unfortunately, the hybrid progeny of Yorkie^CA-overexpressing silkworms and Ras1^CA-overexpressing silkworms did not show overlapping improved silk yield due to the failure to increase expression of both Yorkie and Ras1.

Characterization of Transgenic Silkworm Yielded Biomaterials with Calcium-Binding Activity

Silk fibers have many inherent properties that are suitable for their use in biomaterials. In this study, the silk fibroin was genetically modified by including a Ca-binding sequence, [(AGSGAG)₆ASEYDYDDDSDDDDEWD]₂ from shell nacreous matrix protein. It can be produced as fibers by transgenic silkworm. The Ca-binding activity and mineralization of the transgenic silk fibroin were examined in vitro. The results showed that this transgenic silk fibroin had relatively higher Ca-binding activity than unmodified silk fibroin. The increased Ca-binding activity could promote the usage of silk fibroin as a biomaterial in the pharmaceutical industry. This study shows the possibility of using silk fibroin as a mineralization accelerating medical material by generating genetically modified transgenic silkworm.

Enhancer activity of Helitron in sericin-1 gene promoter from Bombyx mori

Sericin is a kind of water-soluble protein expressed specifically in the middle silk gland of Bombyx mori. When the sericin-1 gene promoter was cloned and a transgenic vector was constructed to express a foreign protein, a specific Helitron, Bmhel-8, was identified in the sericin-1 gene promoter sequence in some genotypes of Bombyx mori and Bombyx mandarina. Given that the Bmhel-8 Helitron transposon was present only in some genotypes, it could be the source of allelic variation in the sericin-1 promoter. The length of the sericin-1 promoter sequence is approximately 1063 or 643 bp. The larger size of the sequence or allele is ascribed to the presence of Bmhel-8. Silkworm genotypes can be homozygous for either the shorter or larger promoter sequence or heterozygous, containing both alleles. Bmhel-8 in the sericin-1 promoter exhibits enhancer activity, as demonstrated by a dual-luciferase reporter system in BmE cell lines. Furthermore, Bmhel-8 displays enhancer activity in a sericin-1 promoter-driven gene expression system but does not regulate the tissue-specific expression of sericin-1.

Processing and characterization of silk sericin from Bombyx mori and its application in biomaterials and biomedicines

Bombyx mori silk is composed of 60-80% fibroin, 15-35% sericin and 1-5% non-sericin component including wax, pigments, sugars and other impurities. For two decades, the protein-based silk fibroin was extensively used in the research and development of medical biomaterials and biomedicines. Sericin is frequently ignored and abandoned as a byproduct or waste in the processing of traditional silk fabrics, silk floss or modern silk biomaterials. However, similar to fibroin, sericin is not only a highly useful biological material, but also a lot of biological activity. Moreover, the non-sericin component present with sericin in the cocoon shell also has a strong biological activity. In this review, the extraction and recovery methods of sericin and the non-sericin component from the cocoon layer are reported, and their composition, properties and biological activity are described to produce a comprehensive report on biomedical materials and biological drugs. In addition, related problems or concerns present in the research and development of sericin are discussed, and a potential application of sericin in sustainable development is also presented.

Large-scale production of bioactive recombinant human acidic fibroblast growth factor in transgenic silkworm cocoons

With an increasing clinical demand for functional therapeutic proteins every year, there is an increasing requirement for the massive production of bioactive recombinant human acidic fibroblast growth factor (r-haFGF). In this present study, we delicately explore a strategy for the mass production of r-haFGF protein with biological activity in the transgenic silkworm cocoons. The sequence-optimized haFGF was inserted into an enhanced sericin-1 expression system to generate the original transgenic silkworm strain, which was then further crossed with a PIG jumpstarter strain to achieve the remobilization of the expression cassette to a “safe harbor” locus in the genome for the efficient expression of r-haFGF. In consequence, the expression of r-haFGF protein in the mutant line achieved a 5.6-fold increase compared to the original strain. The high content of r-haFGF facilitated its purification and large-scald yields. Furthermore, the r-haFGF protein bioactively promoted the growth, proliferation and migration of NIH/3T3 cells, suggesting the r-haFGF protein possessed native mitogenic activity and the potential for wound healing. These results show that the silk gland of silkworm could be an efficient bioreactor strategy for recombinant production of bioactive haFGF in silkworm cocoons.

Targeted glycoengineering extends the protein N-glycosylation pathway in the silkworm silk gland

The silkworm silk glands are powerful secretory organs that can produce and secrete proteins at high levels. As such, it has been suggested that the biosynthetic and secretory power of the silk gland can be harnessed to produce and secrete recombinant proteins in tight or loose association with silk fibers. However, the utility of the silkworm platform is constrained by the fact that it has a relatively primitive protein N-glycosylation pathway, which produces relatively simple insect-type, rather than mammalian-type N-glycans. In this study, we demonstrate for the first time that the silk gland protein N-glycosylation pathway can be glycoengineered. We accomplished this by using a dual piggyBac vector encoding two distinct mammalian glycosyltransferases under the transcriptional control of a posterior silk gland (PSG)-specific promoter. Both mammalian transgenes were expressed and each mammalian N-glycan processing activity was induced in transformed silkworm PSGs. In addition, the transgenic animals produced endogenous glycoproteins containing significant proportions of mammalian-type, terminally galactosylated N-glycans, while the parental animals produced none. This demonstration of the ability to glycoengineer the silkworm extends its potential utility as a recombinant protein production platform.

Identification of Core Alpha 1,3-Fucosyltransferase Gene From Silkworm: An Insect Popularly Used to Express Mammalian Proteins

Silkworm has great potential as production system of recombinant mammalian proteins. When the protein products are used for medical purpose, it is required to reduce the risk of an allergy, the content of core alpha 1,3-fucosyl residue attached to the N-glycan of proteins, for example. We isolated the gene of an enzyme responsible for the transfer of core alpha 1,3-fucosyl residue, core alpha 1,3-fucosyltransferase (Fuc-T C3), from silkworm. A candidate cDNA for silkworm Fuc-T C3 was isolated as a homolog of the fruit fly enzyme gene fucTA. The gene was located on chromosome 7 of the silkworm genome and was composed of seven exons, which spanned approximately 10 kb on the genome. The coding region of the gene was 1,350 bp and encoded a 450-amino acid protein with a molecular mass of 52.2 kDa. Deduced amino acid sequence of the coding region showed one transmembrane domain in its N-terminal and typical motifs common to fucosyltransferases including Fuc-T C3s of other organisms in its C-terminal. The extract of CHO cells transfected with the cDNA showed Fuc-T C3 activity using GDP-fucose and DABS-GnGn peptide as substrates. These results showed this cDNA clone actually encodes silkworm Fuc-T C3.

An efficient strategy for producing a stable, replaceable, highly efficient transgene expression system in silkworm, Bombyx mori

We developed an efficient strategy that combines a method for the post-integration elimination of all transposon sequences, a site-specific recombination system, and an optimized fibroin H-chain expression system to produce a stable, replaceable, highly efficient transgene expression system in the silkworm (Bombyx mori) that overcomes the disadvantages of random insertion and post-integration instability of transposons. Here, we generated four different transgenic silkworm strains, and of one the transgenic strains, designated TS1-RgG2, with up to 16% (w/w) of the target protein in the cocoons, was selected. The subsequent elimination of all the transposon sequences from TS1-RgG2 was completed by the heat-shock-induced expression of the transposase in vivo. The resulting transgenic silkworm strain was designated TS3-g2 and contained only the attP-flanked optimized fibroin H-chain expression cassette in its genome. A phiC31/att-system-based recombinase-mediated cassette exchange (RMCE) method could be used to integrate other genes of interest into the same genome locus between the attP sites in TS3-g2. Controlling for position effects with phiC31-mediated RMCE will also allow the optimization of exogenous protein expression and fine gene function analyses in the silkworm. The strategy developed here is also applicable to other lepidopteran insects, to improve the ecological safety of transgenic strains in biocontrol programs.

Advanced silk material spun by a transgenic silkworm promotes cell proliferation for biomedical application

Natural silk fiber spun by the silkworm Bombyx mori is widely used not only for textile materials, but also for biofunctional materials. In the present study, we genetically engineered an advanced silk material, named hSFSV, using a transgenic silkworm, in which the recombinant human acidic fibroblast growth factor (hFGF1) protein was specifically synthesized in the middle silk gland and secreted into the sericin layer to surround the silk fiber using our previously optimized sericin1 expression system. The content of the recombinant hFGF1 in the hSFSV silk was estimated to be approximate 0.07% of the cocoon shell weight. The mechanical properties of hSFSV raw silk fiber were enhanced slightly compared to those of the wild-type raw silk fiber, probably due to the presence of the recombinant of hFGF1 in the sericin layer. Remarkably, the hSFSV raw silk significantly stimulated the cell growth and proliferation of NIH/3T3 mouse embryonic fibroblast cells, suggesting that the mitogenic activity of recombinant hFGF1 was well maintained and functioned in the sericin layer of hSFSV raw silk. These results show that the genetically engineered raw silk hSFSV could be used directly as a fine biomedical material for mass application. In addition, the strategy whereby functional recombinant proteins are expressed in the sericin layer of silk might be used to create more genetically engineered silks with various biofunctions and applications.

Genome editing of BmFib-H gene provides an empty Bombyx mori silk gland for a highly efficient bioreactor

Evolution has produced some remarkable creatures, of which silk gland is a fascinating organ that exists in a variety of insects and almost half of the 34,000 spider species. The impressive ability to secrete huge amount of pure silk protein, and to store proteins at an extremely high concentration (up to 25%) make the silk gland of Bombyx mori hold great promise to be a cost-effective platform for production of recombinant proteins. However, the extremely low production yields of the numerous reported expression systems greatly hindered the exploration and application of silk gland bioreactors. Using customized zinc finger nucleases (ZFN), we successfully performed genome editing of Bmfib-H gene, which encodes the largest and most abundant silk protein, in B. mori with efficiency higher than any previously reported. The resulted Bmfib-H knocked-out B. mori showed a smaller and empty silk gland, abnormally developed posterior silk gland cells, an extremely thin cocoon that contain only sericin proteins, and a slightly heavier pupae. We also showed that removal of endogenous Bmfib-H protein could significantly increase the expression level of exogenous protein. Furthermore, we demonstrated that the bioreactor is suitable for large scale production of protein-based materials.

Functional characterization of the vitellogenin promoter in the silkworm, Bombyx mori

Genetic transformation and genome editing technologies have been successfully established in the lepidopteran insect model, the domesticated silkworm, Bombyx mori, providing great potential for functional genomics and practical applications. However, the current lack of cis-regulatory elements in B. mori gene manipulation research limits further exploitation in functional gene analysis. In the present study, we characterized a B. mori endogenous promoter, Bmvgp, which is a 798-bp DNA sequence adjacent to the 5'-end of the vitellogenin gene (Bmvg). PiggyBac-based transgenic analysis shows that Bmvgp precisely directs expression of a reporter gene, enhanced green fluorescent protein (EGFP), in a sex-, tissue- and stage-specific manner. In transgenic animals, EGFP expression can be detected in the female fat body from larval-pupal ecdysis to the following pupal and adult stage. Furthermore, in vitro and in vivo experiments revealed that EGFP expression can be activated by 20-hydroxyecdysone, which is consistent with endogenous Bmvg expression. These data indicate that Bmvgp is an effective endogenous cis-regulatory element in B. mori.

The advances and perspectives of recombinant protein production in the silk gland of silkworm Bombyx mori

The silk gland of silkworm Bombyx mori, is one of the most important organs that has been fully studied and utilized so far. It contributes finest silk fibers to humankind. The silk gland has excellent ability of synthesizing silk proteins and is a kind tool to produce some useful recombinant proteins, which can be widely used in the biological, biotechnical and pharmaceutical application fields. It's a very active area to express recombinant proteins using the silk gland as a bioreactor, and great progress has been achieved recently. This review recapitulates the progress of producing recombinant proteins and silk-based biomaterials in the silk gland of silkworm in addition to the construction of expression systems. Current challenges and future trends in the production of valuable recombinant proteins using transgenic silkworms are also discussed.

Basic helix-loop-helix transcription factor Bmsage is involved in regulation of fibroin H-chain gene via interaction with SGF1 in Bombyx mori

Silk glands are specialized in the synthesis of several secretory proteins. Expression of genes encoding the silk proteins in Bombyx mori silk glands with strict territorial and developmental specificities is regulated by many transcription factors. In this study, we have characterized B. mori sage, which is closely related to sage in the fruitfly Drosophila melanogaster. It is termed Bmsage; it encodes transcription factor Bmsage, which belongs to the Mesp subfamily, containing a basic helix-loop-helix motif. Bmsage transcripts were detected specifically in the silk glands of B. mori larvae through RT-PCR analysis. Immunoblotting analysis confirmed the Bmsage protein existed exclusively in B. mori middle and posterior silk gland cells. Bmsage has a low level of expression in the 4th instar molting stages, which increases gradually in the 5th instar feeding stages and then declines from the wandering to the pupation stages. Quantitative PCR analysis suggested the expression level of Bmsage in a high silk strain was higher compared to a lower silk strain on day 3 of the larval 5th instar. Furthermore, far western blotting and co-immunoprecipitation assays showed the Bmsage protein interacted with the fork head transcription factor silk gland factor 1 (SGF1). An electrophoretic mobility shift assay showed the complex of Bmsage and SGF1 proteins bound to the A and B elements in the promoter of fibroin H-chain gene(fib-H), respectively. Luciferase reporter gene assays confirmed the complex of Bmsage and SGF1 proteins increased the expression of fib-H. Together, these results suggest Bmsage is involved in the regulation of the expression of fib-H by being together with SGF1 in B. mori PSG cells.

Expression system for production of bioactive compounds, recombinant human adiponectin, in the silk glands of transgenic silkworms

Adiponectin is an adipocyte hormone involved in glucose and lipid metabolism. The aim of this study was to develop a human adiponectin expression system in transgenic silkworm using a human adiponectin expression vector. The silk gland of the silkworm is a highly specialized organ that has the wonderful ability to synthesize and secrete silk protein. To express human adiponectin in the silk gland of transgenic silkworm, targeting vectors pB-A3-adiponectin-IRES-RFP and pB-Ser1-adiponectin-IRES-RFP were constructed and then introduced into the silkworm pupa. The transgenic silkworms were verified by PCR and then generated. The level of adiponectin in the transgenic silkworm was 6-10 ng/50 mg of freeze-dried powder, and western blotting using an antibody against human adiponectin demonstrated a specific band with a molecular weight of 30 kDa in the silkworm. These results showed that human adiponectin introduced into the silkworm genome was expressed successfully on a large-scale.

An optimized sericin-1 expression system for mass-producing recombinant proteins in the middle silk glands of transgenic silkworms

The middle silk gland (MSG) of silkworm is thought to be a potential host for mass-producing valuable recombinant proteins. Transgenic MSG expression systems based on the usage of promoter of sericin1 gene (sericin-1 expression system) have been established to produce various recombinant proteins in MSG. However, further modifying the activity of the sericin-1 expression system to yield higher amounts of recombinant proteins is still necessary. In this study, we provide an alternative modification strategy to construct an efficient sericin-1 expression system by using the hr3 enhancer (hr3 CQ) from a Chongqing strain of the Bombyx mori nuclear polyhedrosis virus (BmNPV) and the 3'UTRs of the fibroin heavy chain (Fib-HPA), the fibroin light chain (Fib-LPA), and Sericin1 (Ser1PA) genes. We first analyzed the effects of these DNA elements on expression of luciferase, and found that the combination of hr3 CQ and Ser1PA was most effective to increase the activity of luciferase. Then, hr3 CQ and Ser1PA were used to modify the sericin1 expression system. Transgenic silkworms bearing these modified sericin1 expression vectors were generated by a piggyBac transposon mediated genetic transformation method. Our results showed that mRNA level of DsRed reporter gene in transgenic silkworms containing hr3 CQ and Ser1PA significantly increased by 9 fold to approximately 83 % of that of endogenous sericin1. As the results of that, the production of recombinant RFP increased by 16 fold to 9.5 % (w/w) of cocoon shell weight. We conclude that this modified sericin-1 expression system is efficient and will contribute to the MSG as host to mass produce valuable recombinant proteins.

Spatial immobilization of bone morphogenetic protein-4 in a collagen-PLGA hybrid scaffold for enhanced osteoinductivity

The introduction of bioactive molecules into three-dimensional porous scaffolds to mimic the in vivo microenvironment is a promising strategy for tissue engineering and stem cell research. In this study, bone morphogenetic protein-4 (BMP4) was spatially immobilized in a collagen-PLGA hybrid scaffold with a fusion BMP4 composed of an additional collagen-binding domain derived from fibronectin (CBD-BMP4). CBD-BMP4 bound to the collagen-PLGA hybrid scaffold and the BMP4-immobilized hybrid scaffold supported cell adhesion and proliferation. The osteogenic induction effect of the immobilized CBD-BMP4 was investigated with three-dimensional culture of human bone marrow-derived mesenchymal stem cells in the BMP4-immobilized collagen-PLGA hybrid scaffold. The in vivo implantation experiment demonstrated that the immobilized CBD-BMP4 maintained its osteoinductive activity, being capable of up-regulating osteogenic gene expression and biomineralization. The strong osteoinductivity of the BMP4-immobilized scaffold suggests it should be useful for bone tissue engineering, stem cell function manipulation and bone substitutes.

Novel enhancer and promoter elements indispensable for the tissue-specific expression of the sericin-1 gene of the silkworm Bombyx mori

Sericins are glue proteins produced specifically in the middle silk gland (MSG) of the silkworm Bombyx mori, while the silk fiber protein, fibroin, is produced in the posterior silk gland (PSG). These silk proteins are expected to be useful biomaterials in medical technology as well as biotechnology. In this study, we analyzed promoter elements of the sericin-1 gene (ser1) in vivo by introducing reporter constructs into silk glands via gene gun technology. The region from -1602 to +47 was sufficient to induce MSG-specific expression. The 5' deletion mutants showed a three-step decrease in promoter activity with the key sequences located between -1362 and -1250, -201 and -116, and -115 and -37. We detected a tissue- and stage-specific factor complex (MSG-intermolt-specific complex: MIC) bound to the sequence elements around the -1350, -320, -180, and -70 regions. A mutation in the -70 region, which inhibits MIC-binding, diminished almost all promoter activity, while another mutation that did not inhibit MIC-binding showed no effect on promoter activity. The results suggest that the binding of MIC to the above elements is intrinsic for the spatiotemporal specificity of ser1 in vivo.

A cell free assay system estimating the neutralizing capacity of GM-CSF antibody using recombinant soluble GM-CSF receptor

BACKGROUNDS

Previously, we demonstrated that neutralizing capacity but not the concentration of GM-CSF autoantibody was correlated with the disease severity in patients with autoimmune pulmonary alveolar proteinosis (PAP)¹⁻³. As abrogation of GM-CSF bioactivity in the lung is the likely cause for autoimmune PAP⁴⁻⁵, it is promising to measure the neutralizing capacity of GM-CSF autoantibodies for evaluating the disease severity in each patient with PAP. Until now, neutralizing capacity of GM-CSF autoantibodies has been assessed by evaluating the growth inhibition of human bone marrow cells or TF-1 cells stimulated with GM-CSF⁶⁻⁸. In the bioassay system, however, it is often problematic to obtain reliable data as well as to compare the data from different laboratories, due to the technical difficulties in maintaining the cells in a constant condition.

OBJECTIVE

To mimic GM-CSF binding to GM-CSF receptor on the cell surface using cell-free receptor-binding-assay.

METHODS

Transgenic silkworm technology was applied for obtaining a large amount for recombinant soluble GM-CSF receptor alpha (sGMRα) with high purity⁹⁻¹³. The recombinant sGMRα was contained in the hydrophilic sericin layers of silk threads without being fused to the silk proteins, and thus, we can easily extract from the cocoons in good purity with neutral aqueous solutions¹⁴(,)¹⁵. Fortunately, the oligosaccharide structures, which are critical for binding with GM-CSF, are more similar to the structures of human sGMRα than those produced by other insects or yeasts.

RESULTS

The cell-free assay system using sGMRα yielded the data with high plasticity and reliability. GM-CSF binding to sGMRα was dose-dependently inhibited by polyclonal GM-CSF autoantibody in a similar manner to the bioassay using TF-1 cells, indicating that our new cell-free assay system using sGMRα is more useful for the measurement of neutralizing activity of GM-CSF autoantibodies than the bioassay system using TF-1 cell or human bone marrow cells.

CONCLUSIONS

We established a cell-free assay quantifying the neutralizing capacity of GM-CSF autoantibody.

Sustained-release of protein from biodegradable sericin film, gel and sponge

A silk protein, sericin, contains 18 kinds of amino acids, mostly polar side chains forming a complex of three principal polypeptides. The major polypeptides exhibit hydrophobic characteristics by forming a β-sheet structure in a hydrate state. As a drug-releasing biomaterial made by an aqueous process without using any cross linker, sericin is expected to form various hydrophobic dosage forms. However, its dosage form, with respect to the molecular weight and concentration of sericin, and its biodegradation behavior has not been studied in detail. In this study, the film, gel and sponge of sericin were prepared and examined to determine the release properties of the charged protein, fluorescein isothiocyanate-albumin (FA). The film and gel, as solid and semisolid forms, respectively, were also evaluated for their biodegradation behavior. For in vitro release, FA was sustained-released from these preparations. The concentration and dosage form markedly affected FA release. For in vivo biodegradation, the sericin preparations implanted subcutaneously in rats gradually decreased in size and weight. Histological examination indicated no marked inflammation at the site. As for in vivo release, FA remained for 3-6 weeks or more in rats. These findings suggest that sericin is suitable for use as a drug-releasing biomaterial.